This invention lies in the field of electrical charging devices, such as fence chargers, which produce a series of timed short-time-duration pulses, of high voltage, to be applied to wire fences, for the control of animals.
More particularly this invention lies in the field of voltage chargers for the protection of electrical insulated cables from damage by animals.
Still more particularly this invention described a type of voltage charger that can be applied to the protection of electrical cables from damage by animals.
In the prior art, it has been customary to control large field animals by setting up an insulated wire fence surrounding an enclosure, and applying to the insulated wires an electrical, pulsating voltage, of high enough voltage, to electrically shock the animal whenever it contacts the wire. The shock is not enough to injure the animal, but it is enough to discourage it from approaching the wire.
Commercial "fence charger" devices have been on the market for many years for charging such fences.
In the seismic geophysical field of exploration for minerals in the earth, long, multiconductor cables have been deployed along the ground for the purpose of connecting geophones to amplifiers, etc. Since these cables are often 5-10 miles in length, it is impossible to police the area to drive animals away that might bite into the cables, and cause breaks in the conductors.
In some undeveloped areas of the country, severe damage to the cables is experienced, particularly from small animals, such as rodents.
The referenced U.S. Pat. No. 3,878,444 describes an improved type of cable construction, which in conjunction with a suitable source of pulsating voltage connected to a shield under the jacket, has been found to effectively deter animals from biting or otherwise harming the cables.
The big problem has been the provision of a suitable voltage source. When the conventional fence charger was used to charge the cable, it was found that the conventional fence charger is a generator with high internal impedance, whereas the cable shield has a high capacitance to ground, and therefore has a low impedance to ground. Consequently, when the "fence charger" is used to charge the cable, the voltage output drops to a small fraction of the voltage it delivers when charging a fence wire, because the fence wire has a high impedance to ground.
In view of the impedance mismatch of the fence charger to the cable, it was determined that what was needed was a charger that had a low internal impedance, and which could deliver a high voltage into the low impedance of the cable.
To do this requires a large power source, and such a power source is not readily available. The best type of power source that can be left unattended 24 hours a day is an electrical battery. Even so, the handling of heavy batteries and the problem of keeping them charged, is such a difficult procedure in the field, that the power drain must be kept to a minimum.
In seismic operations, variable lengths of cable are often required, and since the impedance to ground of the actual cable depends on its length, the load impedance on the cable charger may vary from day to day.
Therefore means must be provided for setting a time schedule of voltage pulses that will be frequent enough to ensure that the animal will feel the shock no matter how short the contact time. Also means must be provided to ensure that the pulse voltage reaches a selected value of voltage E. And further, means must be provided to terminate the pulse as shown as the selected voltage E is reached, in order to minimize the power drain from the battery or other power source.
It is therefore a primary object of this invention to provide a source of high voltage which repetitively generates a high d.c. voltage pulse.
It is a further object to ensure that the output voltage reaches the selected value of voltage E irrespective of the load impedance of the cable to which it is attached.
It is still a further object of this invention to provide means for terminating the pulse as soon as possible after it reaches the selected value of voltage E.